1. Field of the Invention
The invention relates to a ring bearing for use in a MacPherson strut, and more particularly to a ring bearing made of plastic.
2. Background Art
As shown in FIG. 1, a MacPherson strut assembly has a strut tube 5, and a lower spring seat 4 welded to the strut tube 5. A spring 6 is positioned directly on the spring seat 4, or may be seated in a rubber dampener which is positioned on the spring seat 4. The latter reduces the road vibration transmitted from the wheels. The upper end of the spring 6 is held by the upper spring seat 1 which can also utilize a rubber dampening medium 3. A bearing 2 is captured in the upper spring seat 1 and keeps the upper seat 1 concentric to the strut tube 5. The upper seat 1 is interference fitted into the bore of the bearing 2.
An example of a known bearing 2 is described in detail in connection with FIG. 2. It supports the loads which are transferred through the spring 4 in a dual path arrangement and supports the loads from the spring 4 and strut tube 5 in a single path system.
The bearing 2 (FIG. 2) comprises upper and lower plastic casings 8 and 9. The arm extensions 8a, 8b, 8c, 8d, 9a, 9b provide a sealing function and on one side (8d) a locking feature. A set of balls 10 ride on two hardened steel raceways 11a, 11b. The raceways may be shaped corresponding to the curvature of the balls 10, or may be stamped in approximately a Gothic arch shape, for example. The latter shape provides for axial and radial load-carrying capacity. It also eliminates side movement in the bearing, which eliminates the fouling of the upper and lower plastic casings.
Another known bearing 2a (FIG. 3) is comprised of an upper hardened steel raceway 12 which is stamped to form an angular contact bearing 2a. A set of balls 10 are held by a lower hardened steel raceway 13 which is covered partially in rubber 14. The rubber 14 provides a sealing function on the inner and outer surfaces. An inner lip 15 of the lower raceway 13 seats into a groove 16 in the upper raceway 12. This locks the bearing 2a together.
As described above, the known designs utilize steel balls in associated steel raceways. The raceways and balls are held in place and protected from contamination by upper and lower plastic casings, which lock together by the use of angled lips or extensions which can be on both the outer and inner portions of the upper and lower casings.
Despite the general success of these designs, there is a continuing need to reduce the manufacturing cost of the bearing and the weight of the bearing assembly, without altering its overall size.